Tissue destruction which often accompanies the protracted presence of a chronic inflammatory infiltrate may be a direct consequence of interactions between components of the exudate and external stimuli. The mononuclear phagocyte, a prominent component of inflammatory exudates has recently been implicated in the production of several substances which may have profound qualitative and quantitative effects on the progression of tissue destruction in the inflamed tissues of periodontitis and other inflammatory diseases. The principal objective of this proposal is to isolate pure populations of normal human peripheral blood monocytes and measure in culture their capacity to respond to a variety of stimuli by synthesizing and secreting tissue lytic substances. The stimuli to be employed include components of and substances likely to be produced by microorganisms found in dental plaque, components of the complement system, and antigen-antibody complexes. Responses of interest include the specific synthesis and release of lysosomal enzymes, bone resorbing factors, complement and neutral proteases such as collagenase. Centrifugal elutriation will be employed as the principal technique for the isolation of mononuclear phagocytes from other blood cells. This technique produces pure populations of cells prior to introduction into culture. In vitro the cells, cultured under defined conditions (serum-free) will be systematically treated with known quantities of the desired stimulants and the several assays for biologically active substances performed on the culture media and/or lysates of the cells.